Nowadays power generation from solar energy, i.e., photovoltaic generation, is widely applied domestic and overseas. The grid-connected type of the photovoltaic system mainly includes a photovoltaic array, a junction box, an inverter, and etc. In US, PV system circuits installed on or in buildings shall include a rapid shutdown function to reduce shock hazard for emergency responders in accordance with NEC (National Electrical Code), article 690.12.
In the conventional grid-connected type of the photovoltaic system, a rapid shutdown device may be present between the photovoltaic array and the inverter, so as to avoid increasing the difficulty to the rescuers, even making a threat to the life safety of the rescuers, due to breakage and leakage of input wires of the photovoltaic array caused by the emergency accidents.
FIG. 1 is a structural schematic diagram of a photovoltaic system. As shown in FIG. 1, the photovoltaic system 1 includes a photovoltaic array 10, a PV shutdown device 100, a junction box 102 and an inverter 101. The photovoltaic array 10 converts the solar energy into DC electrical energy, and transfers the DC electrical energy to the inverter 101 via high voltage wires. The inverter 101 converts the DC power to AC power and deliver it to the installed wire. The junction box 102 is used for configuring lead wires at an input side and an output side of the inverter 101. The PV shutdown device 100 is used for disconnecting the high voltage wire from the photovoltaic array 10 and the junction box 102 when shut down action is initiated, such that the photovoltaic array 10 and the inverter 101 are disconnected.
In the photovoltaic system 1 shown in FIG. 1, a plurality of photovoltaic arrays 10 share a same PV shutdown device 100, such that the same one PV shutdown device 100 controls a shutdown and a closure of a plurality of high voltage wires between the plurality of photovoltaic arrays 10 and the junction box 102. As shown in FIG. 1, one signal wire 103 is laid between the junction box and the inverter, and when shut down action is initiated, the inverter 101 transfers the control signal to the junction box via the signal wire 103. A signal wire 104 is drawn out from the junction box to the PV shutdown device, and the junction box outputs the control signal SELV1 to the PV shutdown device via the signal wire 104, so as to control the shutdown of the PV shutdown device. However, since the rapid shutdown device itself has lead wires for all DC high voltage outputted by the photovoltaic arrays, it is difficult to ensure the requirement that a distance between the PV photovoltaic arrays and the rapid shutdown device can meet the requirement of National Electrical Code (NEC).
FIG. 2 is a structural schematic diagram of another photovoltaic system. As shown in FIG. 2, the photovoltaic system 2 includes a photovoltaic array 20, a PV shutdown device 200, a junction box 202 and an inverter 201. As compared with FIG. 1, in FIG. 2, each photovoltaic array 20 and the junction box 202 are installed with one PV shutdown device 200. As shown in FIG. 2, one signal wire 203 is laid between the junction box and the inverter, and when shut down action is initiated, the inverter 201 transfers the control signal to the junction box via the signal wire 203. The junction box draws out a signal wire 204 to each PV shutdown device, and the control signal is output to the PV shutdown device so as to control the shutdown of each PV shutdown device.
No matter what kind of the above-mentioned photovoltaic system is, the difficulty and complexity of installing the system will increase.
Meanwhile, with respect to the provisions about PV Rapid shutdown Systems in UL 1741 CRD, it is required that the rapid shutdown device has a self-test functionality, and one self-test is carried out periodically, and when the self-test is not passed, an obvious instruction or an alarm sound is necessary to achieve a warning function. In order to satisfy the principle that the rapid shutdown device is as close to a PV panel of the photovoltaic array as possible, such warning function is generally implemented in a body of the inverter or in the junction box. With the shutdown device mentioned before, it is hard to achieve as there is no communication between the shutdown device and inverter or the accessory. To achieve this, it is necessary to add more connection between the shutdown device on the roof nearby the PV array and inverter or accessory, this will increase the system cost and complexity.